Glass is installed in the front surface of a display device, such as an LCD or an LED, in portable terminals including smart phones which recently come into use. Furthermore, a specific function is designed to be executed by touching front glass because a touch pad function is included in such a display device. Furthermore, such front glass is also widely applied to home appliances, such as TV, and an electronic device for vehicle, such as a navigator, in addition to a smart phone and a personal terminal, such as a touch pad having a specific function. Furthermore, in the case of a smart phone having a touch pad function, such front glass is also called touch window glass.
Such front glass is applied to products as 2D glass commonly having a plane shape. Recently, the front glass of TV, that is, one of home appliances, is generally formed into a curved surface or into a curved surface having curves on both sides thereof on the basis of a single axis. The glass of a smart phone is also formed of curved surface glass having various types. Furthermore, glass formed to have a curved surface as described above in a smart phone is commonly called 3D glass.
Furthermore, for example, the 3D glass of a smart phone may be formed into a curved surface with respect to any one of an X axis and a Y axis on the XY plane. Furthermore, although the 3D glass is formed to have a curved surface with respect to a single axis as described above, front glass may be generally formed into a curved surface or edges on both sides may be formed into a curved surface. Furthermore, the 3D glass may be formed into a curved surface with respect to the X axis and the Y axis, that is, the two axes. Alternatively, the central part of the 3D glass may be formed to have a plane, and only the edge part thereof may be formed to have a curved surface. Furthermore, the entire 3D glass may be formed into a curved surface.
As shown in FIG. 1, 3D glass having a curved surface as described above is commonly formed by an upper mold Da and a lower mold Db. That is, the shape of the 3D glass is determined by the shape of a cavity formed between the upper mold Da and the lower mold Db. If such an upper mold and a lower mold are placed in a high temperature atmosphere, 3D glass Gb corresponding to the cavity between the upper mold Da and the lower mold Db is produced from a plane shaped glass Ga.
Regarding the forming of the curved surface of front glass which may be used for a portable terminal or home appliances, some mold were suggested by Japanese Patent Application Publication No. 2007-534596. However, the Japanese prior art did not mention any apparatus capable of mass production. Furthermore, Korean Patent No. 10-1449364 issued to the present applicant discloses a forming apparatus using an endless conveyer for mass production. However, the forming apparatus does not disclose an element for preventing oxidization during mass production or an element for enabling the forming apparatus to reliably operate for a long term with respect to a change attributable to thermal expansion and thermal contraction.